1. Field of the Invention
This invention relates to a process for the production of light-colored, low-viscosity surfactant concentrates by mixing sugar surfactants and betaines in the gel phase.
2. Description of the Related Art
Alkyl oligoglycosides, more particularly alkyl oligoglucosides, are nonionic surfactants which are acquiring increasing significance by virtue of their excellent detergent properties and their high ecotoxicological compatibility. The production and use of these substances have been described just recently in a number of synoptic articles of which those by H. Hensen in Skin Care Forum, (October 1992), D. Balzer and N. Ripke in Seifen-Ole-Fette-Wachse 118, 894 (1992) and B. Brancq in Seifen-Ole-Fette-Wachse 118, 905 (1992) are cited as representative. Equally favorable properties are known to be exhibited by a second group of sugar surfactants, namely fatty acid-N-alkyl polyhydroxyalkylamides, more particularly fatty acid-N-alkyl glucamides.
In some respects, however, the use of sugar surfactants is attended by problems. For example, it is not possible to produce pumpable aqueous concentrates with a solids content above 40% by weight without the sugar component undergoing partial decomposition in the course of the concentration process. In addition, the glycosides and glucamides share this property with most anionic surfactants which form a viscous gel phase above an active substance content of around 35% by weight. In addition, sugar surfactants have a tendency to crystallize during storage at low temperatures which is a significant obstacle to their subsequent use.
The use of sugar surfactants of the types mentioned above together with amphoteric or zwitterionic surfactants of the betaine type in surface-active formulations is known in principle from the prior art.
Mixtures of--albeit short-chain--alkyl glucosides and alkyl amidobetaines or imidazolinium betaines were disclosed for the first time in an article by G. Proserpio et al in Rivista Italiana 56, 567 (1974). EP-A 0 075 994 (Procter & Gamble) describes combinations of alkyl glucosides with amine oxides, unsaturated soaps, water-soluble builders and selected anionic surfactants. In addition, the mixtures may contain amphoteric surfactants, for example betaines of the 6-(N-dodecylbenzyl-N,N-dimethylammonium)-hexanoate type. U.S. Pat. No. 4,668,422 (Henkel Corp.) discloses liquid soaps and foam baths containing alkyl glucosides, betaines and amine oxides. EP-A-0 250 181 (Helene Curtis) relates to liquid detergents containing alkyl glucosides, anionic surfactants and selected amphoteric surfactants of betaine structure. Surfactant combinations containing alkyl glucosides, alkyl sulfates, betaines and/or amine oxides and optionally alkanolamides are disclosed in EP-A 0 341 071 (Unilever). Manual dishwashing detergents containing alkyl glucosides, fatty alcohol sulfates, fatty alcohol ether sulfates and betaines are known from EP-A 0 513 138, DE-A1 42 34 487 and DE-A1 43 11 114 (all Henkel). Mild shampoos based on alkyl glucosides, anionic surfactants and betaines are described in EP-A 0 453 238 (Unilever). Finally, EP-A 0 508 507 (Berol Nobel) relates to liquid detergents containing alkyl glucosides, anionic surfactants and selected amphoteric surfactants of betaine structure. However, all these publications are concerned with dilute water-containing surfactant mixtures or formulations and not with concentrates.
The use of fatty acid-N-alkyl polyhydroxyalkylamides is also the subject of a number of publications. For example, their use as thickeners is known from European patent application EP-A1 0 285 768 (Huls). FR-A 1 580 491 (Henkel) describes water-containing detergent mixtures based on sulfates and/or sulfonates, nonionic surfactants and optionally soaps which contain fatty acid-N-alkyl glucamides as foam regulators. Mixtures of short-chain and relatively long-chain glucamides are described in DE-C1 44 00 632 (Henkel). In addition, DE-A1 42 36 958 and DE-A1 43 09 567 (Henkel) report on the use of glucamides containing relatively long alkyl chains as pseudoceramides in skin-care formulations and on combinations of glucamides with protein hydrolyzates and cationic surfactants in hair-care products.
International patent application WO 92/06153; WO 92/06156; WO 92/06157; WO 92/06158; WO 92/06159 and WO 92/06160 (Procter & Gamble) relate to mixtures of fatty acid-N-alkyl glucamides with anionic surfactants, sulfate and/or sulfonate surfactants, ether carboxylic acids, ether sulfates, methyl ester sulfonates and nonionic surfactants. The use of these substances in various laundry detergents, dishwashing detergents and cleaning formulations is described in international patent applications, WO 92/06152; WO 92/06154; WO 92/06155; WO 92/06161; WO 92/06162, WO 92/06164, WO 92/06170, WO 92/06171 and WO 92/06172 (Procter & Gamble).
There is a need on the market for concentrated surfactant mixtures based on alkyl and/or alkenyl oligoglucosides which are flowable and pumpable despite a solids content of more than 30% by weight and preferably of the order of 50 to 60% by weight and which have a significantly reduced tendency to crystallize, i.e. improved stability in storage. Since surfactant compounds of the type in question are mainly used in manual dishwashing detergents and hair shampoos, skin-cosmetic or rather dermatological compatibility is also extremely important.
Surfactant concentrates are a particularly favorable commercial formulation for manufacturers and users because they have been minimized in terms of their water content and hence incur lower transport and storage costs. Nevertheless, it is desirable that the surfactant concentrates should have a sufficiently high viscosity in the final formulations, which are of course heavily diluted and have a solids content of 20 to 30% by weight, and should readily lend themselves to thickening using known additives.
Accordingly, the complex problem addressed by the present invention was to provide light-colored, pumpable water-containing surfactant concentrates with high dermatological compatibility based on alkyl glycosides or fatty acid glucamides and betaines which would be distinguished by high stability in storage and which would have a Brookfield viscosity of at most 10,000 mPa.multidot.s and a solids content of 40 to 60% by weight.